Mathematical models for the following phenomena were studied: 1) The elastic properties of a cylindrical membrane under large stretch, applied to sarcolemma and perineurium. 2) The effect of including a series elastic element on the optimal control of a muscle model. 3) The spread of the electrical potential signal over the surface of the dendritic tree of an isolated neuron in tissue culture, resulting from the injection of a sinusoidal current into the cell body.